As is well known, lawn mowing vehicles having reel units are classified roughly into lawn mowing vehicles that mow a lawn when manipulated by a worker, and lawn mowing vehicles that automatically mow a lawn without manipulation of a worker (automatic lawn mowing vehicles). The former lawn mowing vehicles are generally classified into hand-driven type (walk-behind type) lawn mowing vehicles that are operated by a worker located at the rear thereof, and riding lawn mowing vehicles that are operated by a worker who boards the vehicle, and mow a lawn while traveling according to the operation of the worker. In contrast, the latter lawn mowing vehicles (automatic lawn mowing vehicles) travel according to a result of determination of a travel path or a lawn mowing situation that is previously set, and thus automatically mow a lawn without the operation of the worker.
The automatic lawn mowing vehicle typically has a larger area in which a lawn can be mowed in one pass than the hand-driven type lawn mowing vehicle. As such, the hand-driven type lawn mowing vehicle is often used to mow a lawn of a narrow range (e.g., a private yard) or to precisely mow a lawn of each green in a golf course, and a riding lawn mowing vehicle is often used to mow a lawn with a wide range (e.g. greens in a golf course or a sports ground).
An example of the hand-driven type lawn mowing vehicle is disclosed in U.S. Pat. No. 7,111,443, in which a motor is driven by power supplied from a battery, and a lawn mowing unit is operated by a driving force of the motor. Further, an example of a lawn mowing unit is disclosed in Published Japanese Translation No. H05-503207 of the PCT International Publication, which includes an adjustment mechanism capable of adjusting a mowing height of grass, without complicating or interfering with the mechanism.
An example of the riding lawn mowing vehicle is disclosed in Japanese Unexamined Patent Application, First Publication No. 2000-139157, which is configured to be able to move up and down reel units using hydraulic cylinders. In detail, the riding lawn mowing vehicle is allowed to switch back pressure for elevating cylinders, which move up and down three reel units disposed in the front of the vehicle, depending on the slope or unevenness of a working surface, thereby realizing stable work with mowing the lawn while still maintaining a traveling speed without delay of downward movement of the reel units.
Such a riding lawn mowing vehicle is disclosed in Japanese Unexamined Patent Application, First Publication No. H09-074818 (hereinafter “JP-H09-074818”), in which a plurality of electrode parts detecting cropped traces are installed on a bottom portion of the vehicle; a change in voltage between when the electrode parts are electrically conducted by contact with grass and when the electrode parts are insulated by non-contact with the grass is detected; and a cropped-trace boundary that is a boundary between an uncropped area and a cropped area is detected using the detected result. Further, an automatic travel working vehicle is disclosed in Japanese Unexamined Patent Application, First Publication No. S62-070916, in which a predetermined range in front of the vehicle is captured by a camera during radiating strobe light, and predetermined treatment is performed on a captured image, thereby detecting a boundary between an untreated work area and a treated work area. Furthermore, a method of classifying vitality of vegetation into “soundness,” “caution,” “warning,” and “diseased” from a histogram obtained by analyzing reflection information (brightness information image) from the vegetation caught by a video camera, and evaluating a variation in the vitality of vegetation which is easily understood by a human being is disclosed in Japanese Unexamined Patent Application, First Publication No. 2004-213627.
Such an automatic lawn mowing vehicle is disclosed in Japanese Patent No. 2896017 (hereinafter “JP 2896017”), which is configured so as to be able to discriminate a boundary located on each of left and right sides of a vehicle body (a boundary between a treated work area in which a lawn has been mowed and an untreated work area in which a lawn has not been mowed), and to automatically balance positions in a widthwise direction of the vehicle body with regard to these boundaries, thereby enabling a lawn to be properly mowed.
Further, an example of the riding lawn mowing vehicle is disclosed in Japanese Unexamined Patent Application, First Publication No. H11-089377 (hereinafter “JP-H11-089377”), in which reel units are elevated using hydraulic cylinders. In detail, the riding lawn mowing vehicle includes three reel units disposed in the front thereof and two reel units disposed on left and right sides thereof When the reel units are lowered, oil channels for the hydraulic cylinders, which elevate the two reel units disposed on left and right sides of the vehicle, are blocked to prevent the two reel units from being lowered. Thereby, a mowing width can be narrowed.